High-purity copper flat wire, preparation method and application thereof

Abstract

The embodiment of the application discloses a kind of high-purity oxygen-free copper flat wire and its preparation method and application.The preparation method of the high-purity oxygen-free copper flat wire includes: continuously extruding high-purity oxygen-free copper rod with equal diameter, keeping the diameter of copper rod unchanged after large deformation by shearing, obtaining ultra-fine-grained copper rod;Continuous extrusion is carried out to obtain fine-grained copper flat wire;Small deformation drawing at room temperature is carried out to obtain copper flat wire with uniform structure in edge and core;Recovery annealing is carried out to obtain copper flat wire.The application improves the electrical conductivity of the copper flat wire without reducing its mechanical properties, and obtains high-purity oxygen-free copper flat wire with excellent mechanical and electrical properties, providing a material basis for the safe and stable operation of ultra / extra-high voltage transformers.

Description

Technical Field

[0001] This invention relates to the field of rolling processing technology, specifically to a high-purity copper flat wire, its preparation method, and its application. Background Technology

[0002] As crucial equipment for power transmission and transformation, the stability of ultra-high voltage (UHV) and extra-high voltage (EHV) transformers has always been a focus of industry attention. Pure copper enameled wire, as one of their key components, has been a top priority for the power industry in terms of improving its overall conductivity and mechanical properties. Currently, the pure copper enameled wire used in UHV and EHV transformers primarily improves conductivity by increasing copper purity and enhances mechanical properties through deformation strengthening. However, due to their long-term operation at high temperatures, their mechanical properties degrade over time, posing a potential threat to the safe operation of UHV and EHV transformers. Therefore, ensuring the long-term operational stability of pure copper enameled wire while maintaining the required conductivity and mechanical properties is crucial for the safe operation of UHV and EHV transformers.

[0003] Currently, pure copper enameling wires used in ultra-high voltage / extra-high voltage transformers are generally produced using top-drawing continuous casting to manufacture the main rod. Patents CN103406377A and CN101564738A employ a room-temperature drawing process to prepare pure copper flat wires. Patent CN102360635A uses a process of first drawing and then precision rolling to produce pure copper flat wires. When pure copper flat wires prepared by these methods are used in enameling wire production, the deformation strengthening process creates a fibrous structure, generating a large number of dislocations within the pure copper flat wire. This inevitably leads to potential safety and stability risks in transformers during long-term use at certain temperatures. In patent CN106098246A, a composite process of continuous equal channel bend extrusion-room temperature drawing is used to produce copper flat wire. In addition to the problems caused by deformation strengthening, the driving force for forming during the continuous equal channel bend extrusion process depends on the friction between the copper and the extrusion rollers. This results in a significant difference in the flowability of the copper in the core and the edge, which in turn causes differences in the microstructure and properties of the copper flat wire in the core and the edge. This inevitably leads to premature local failure of the final product during use, thereby reducing its service life.

[0004] Therefore, how to obtain fine-grained, uniformly structured, high-purity oxygen-free copper flat wire to achieve a good match between mechanical and electrical properties and meet the conductor requirements of ultra-high voltage / extra-high voltage transformer windings is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] Therefore, embodiments of the present invention provide a high-purity copper flat wire, its preparation method and application. The method of the present invention can effectively control the grain size and fine grain structure uniformity of the pure copper flat wire. The prepared high-purity copper flat wire has excellent mechanical and electrical properties to meet the requirements of ultra-high voltage / extra-high voltage transformer winding wires for copper conductors.

[0006] According to a first aspect of the present invention, a method for preparing high-purity oxygen-free copper flat wire is provided, comprising the following steps:

[0007] S1. High-purity oxygen-free copper rods are subjected to continuous extrusion with equal diameter. After large shear deformation, the diameter of the copper rod remains unchanged to obtain ultrafine-grained copper rods.

[0008] S2. The ultrafine-grained copper rod is continuously extruded to obtain fine-grained copper flat wire;

[0009] S3. The fine-grained copper flat wire is subjected to room temperature small deformation drawing to obtain a copper flat wire with uniform structure at the edge and the core.

[0010] S4. Perform recovery annealing on the flat wire after room temperature deformation to obtain a copper flat wire with matching mechanical properties and electrical conductivity.

[0011] Furthermore, in step S1, the temperature of the continuous extrusion is 100-200℃, the speed of the extrusion roller is 10-15 rpm, and the shear deformation is 80-95%.

[0012] Furthermore, in step S2, the temperature of the continuous extrusion is 400-600℃, the speed of the extrusion roller is 15-20 rpm, and the total deformation is over 90%.

[0013] Furthermore, in step S3, the drawing deformation is carried out at room temperature, with a per-pass deformation of 13-17% and a total deformation of no more than 35%.

[0014] Furthermore, in step S4, the temperature of the recovery annealing is 120-250℃, and the holding time is 20-40 min.

[0015] Furthermore, in step S1, the high-purity oxygen-free copper rod is prepared using an upward drawing method, the specific process of which is as follows:

[0016] The cleaned electrolytic copper plates are evenly fed into an industrial frequency induction furnace for melting at a temperature of 1240-1460℃. The melt is covered with charcoal to a thickness of 40-60mm. The resulting molten copper is then diverted to a holding furnace, where the temperature is controlled at 1120-1150℃. After cooling in a crystallizer, copper rods with a diameter of 8mm-15mm are drawn out.

[0017] According to a second aspect of the present invention, a high-purity oxygen-free copper flat wire is provided, which is made by the method described in any of the preceding claims.

[0018] Furthermore, the high-purity oxygen-free copper flat wire has a copper content ≥99.997wt.%, an oxygen content ≤3ppm, and the sum of the contents of other impurities ≤20ppm.

[0019] Furthermore, the high-purity oxygen-free copper flat wire has a room temperature conductivity of not less than 101% IACS, a yield strength of ≥240MPa, a tensile strength of ≥320MPa, and an elongation of ≥15%.

[0020] According to a third aspect of the present invention, the application of high-purity oxygen-free copper flat wire as described in any of the preceding claims in ultra-high voltage / extra-high voltage transformers is provided.

[0021] The embodiments of the present invention have the following advantages:

[0022] 1. The high-purity oxygen-free copper flat wire provided by this invention has a copper content ≥99.997wt.%, an oxygen content ≤3ppm, and the sum of the contents of other impurities ≤20ppm. According to the test, the high-purity oxygen-free copper flat wire of this invention has a room temperature conductivity ≥101%IACS, a yield strength ≥240MPa, a tensile strength ≥320MPa, and an elongation ≥15%, which can meet the requirements of ultra-high voltage / extra-high voltage transformer winding wires for copper conductors.

[0023] 2. The method for preparing high-purity oxygen-free copper flat wire provided by the present invention adopts the process flow of upward continuous casting-constant diameter continuous extrusion-drawing forming-recovery annealing. By controlling the forming and annealing process conditions, the grain size and structure of pure copper flat wire can be uniformly controlled, and finally high-purity oxygen-free copper flat wire with excellent mechanical and electrical properties can be obtained.

[0024] 3. The method for preparing high-purity oxygen-free copper flat wire provided by this invention employs continuous diameter-continuous extrusion forming of flat wire with equal diameter, which can obtain ultra-fine grain flat wire, thereby improving the mechanical properties of pure copper through fine grain strengthening. Compared with deformation strengthening, fine grain strengthening enhances the stability and reliability of high-purity oxygen-free copper flat wire in actual service. Furthermore, small deformation drawing improves the microstructure inhomogeneity between the edge and core of the continuously extruded copper flat wire, ensuring consistency in the overall performance of the material. Finally, recovery annealing eliminates physical defects caused by deformation, improving the conductivity of the copper flat wire without altering its mechanical properties, thus providing a material basis for the safe and stable operation of ultra-high voltage / extra-high voltage transformers. Attached Figure Description

[0025] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0026] Figure 1 The microstructure morphology of different parts of the high-purity oxygen-free copper flat wire after continuous extrusion in Example 1 of the present invention;

[0027] Figure 2 The stress-strain curves of different parts of the high-purity oxygen-free copper flat wire after continuous extrusion in Example 1 of the present invention are shown under room temperature tensile stress.

[0028] Figure 3 The microstructure morphology of different parts of the high-purity oxygen-free copper flat wire after small deformation drawing in Embodiment 1 of the present invention;

[0029] Figure 4 The stress-strain curve of the high-purity oxygen-free copper flat wire after small deformation drawing in Embodiment 1 of the present invention is shown at room temperature during tensile testing.

[0030] Figure 5 The image shows the microstructure of high-purity oxygen-free copper flat wire after recovery annealing in Example 1 of the present invention, and the stress-strain curves under room temperature tensile stress. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] This embodiment provides a method for preparing high-purity oxygen-free copper flat wire, which includes the following steps:

[0034] (1) High-purity oxygen-free copper rods with a diameter of 12 mm were prepared using conventional upward continuous casting technology. The specific process is as follows: Cleaned electrolytic copper plates were evenly fed into an industrial frequency induction furnace for melting at intervals. The melting temperature was 1250℃, and charcoal was covered on the melt with a thickness of 50 mm. The holding furnace temperature was 1140℃, and the copper rods with a diameter of 12 mm were drawn out after cooling in a crystallizer. Subsequently, continuous extrusion with the same diameter was carried out at an extrusion temperature of 150℃ and an extrusion roller speed of 12 rpm, achieving a shear deformation of 90% to obtain ultrafine-grained copper rods with a diameter of 12 mm.

[0035] (2) The ultrafine copper rods obtained in the above steps were continuously extruded to produce flat wires of 1.64mm*6.62mm. The extrusion temperature was 450℃, the extrusion roller speed was 18 rpm, and the total deformation was 90.39%.

[0036] (3) The copper flat wire obtained by the above steps is drawn to a flat wire of 1.23mm*6.28mm by small deformation. The deformation per pass is 15% and the total deformation is 28.85%, thus obtaining a copper flat wire with uniform structure at the edge and the core.

[0037] (4) The above copper flat wire is subjected to recovery annealing at 240℃ for 25 minutes.

[0038] from Figure 1 (where (a) is the center; (b) is the edge) and Figure 2 It can be seen that the average grain size of the core of the high-purity oxygen-free round copper flat wire after continuous extrusion in Example 1 is 4 μm, and the size distribution is concentrated and uniform. However, the average grain size of the edge is 5.5 μm, and the distribution is uneven, which leads to a significant difference in the mechanical properties of the edge and the core. Figure 3 (where (a) is the center; (b) is the edge) and Figure 4 The microstructure and mechanical properties of the copper flat wire after small deformation drawing are shown. It can be seen that the average grain size of the core and the edge are basically the same, both around 4.5 μm, and the distribution is relatively uniform, with no significant difference in mechanical properties. Figure 5 The microstructure and properties of the copper flat wire after recovery annealing were shown. Compared with the small deformation flat wire, its average grain size did not change significantly. The final yield strength of the copper flat wire was 255 MPa, the tensile strength was 325 MPa, the elongation was 22%, and its conductivity was 101.3% IACS, as listed in Table 1. In addition, Table 2 also shows the impurity content and purity of the high-purity oxygen-free round copper flat wire prepared in Example 1. Combining Tables 1 and 2, it can be seen that the high-purity oxygen-free round copper flat wire prepared in Example 1 can fully meet the requirements of copper conductors for winding wires of ultra-high voltage / extra-high voltage transformers.

[0039] Table 1 Performance of the product in Example 1

[0040] 101.3 255 325 22

[0041] Table 2 Impurity content and purity of the product from Example 1

[0042]

[0043] Example 2

[0044] This embodiment provides a method for preparing high-purity oxygen-free copper flat wire, which includes the following steps:

[0045] (1) High-purity oxygen-free copper rods with a diameter of 8 mm were prepared using conventional upward continuous casting technology. The specific process is as follows: Cleaned electrolytic copper plates were evenly fed into an industrial frequency induction furnace for melting at intervals. The melting temperature was 1250℃, and charcoal was covered on the melt with a thickness of 50 mm. The holding furnace temperature was 1140℃, and the copper rods with a diameter of 8 mm were drawn out after cooling in a crystallizer. Subsequently, continuous extrusion with the same diameter was carried out at an extrusion temperature of 200℃ and an extrusion roller speed of 15 rpm, achieving a shear deformation of 85% to obtain ultrafine-grained copper rods with a diameter of 8 mm.

[0046] (2) The ultrafine copper rods obtained in the above steps were continuously extruded to produce flat wires of 1.08mm*3.85mm. The extrusion temperature was 500℃, the extrusion roller speed was 20 rpm, and the total deformation was 91.72%.

[0047] (3) The copper flat wire obtained by the above steps is drawn to a flat wire of 0.93mm*3.04mm by small deformation. The deformation per pass is 17% and the total deformation is 32.01%, thus obtaining a copper flat wire with uniform structure at the edge and the core.

[0048] (4) The above copper flat wire is subjected to recovery annealing at 180℃ for 35 minutes.

[0049] The obtained high-purity oxygen-free copper flat wire was determined to have a purity of 99.9975% Cu, an oxygen content of 1.5 ppm, and a total content of other impurities not exceeding 18 ppm. Its conductivity is 101.2% IACS, yield strength is 260 MPa, tensile strength is 350 MPa, and elongation is 17%. It fully meets the requirements for copper conductors in winding wires for ultra-high voltage / extra-high voltage transformers.

[0050] Comparative Example 1

[0051] Except for the following, the rest of the content is the same as in Example 1.

[0052] In step (2), the continuous extrusion deformation is 83%.

[0053] Measurements showed that the average grain size of the copper flat wire prepared in this comparative example was 10.5 μm, and it exhibited an uneven microstructure in its core and edges. The copper flat wire prepared in this comparative example had a purity of 99.9975% Cu, an oxygen content of 2.4 ppm, and the total content of other impurities did not exceed 20 ppm. Its conductivity was 101.6% IACS, but its strength and elongation were significantly reduced; specifically, its yield strength was 214 MPa, its tensile strength was 285 MPa, and its elongation was only 10%. Therefore, compared to Example 1, the copper flat wire prepared in this comparative example showed reduced strength and elongation, failing to meet the requirements for copper conductors in ultra-high voltage / extra-high voltage transformer windings.

[0054] Comparative Example 2

[0055] Except for the following, the rest of the content is the same as in Example 1.

[0056] In step (3), the deformation amount of the high-purity oxygen-free copper flat wire during small deformation drawing is 42%.

[0057] Measurements showed that the average grain size of the copper flat wire prepared in this comparative example was 7.6 μm, with a small amount of elongated grains observed in some areas. The copper flat wire prepared in this comparative example had a conductivity of 100.4% IACS, a yield strength of 285 MPa, a tensile strength of 370 MPa, and an elongation of 8%. It is evident that compared to Example 1, the copper flat wire prepared in this comparative example exhibits increased strength, but significantly reduced elongation and conductivity, failing to meet the requirements for copper conductors in ultra-high voltage / extra-high voltage transformer windings.

[0058] Comparative Example 3

[0059] Except for the following, the rest of the content is the same as in Example 1.

[0060] The recovery annealing temperature in step (4) is 380℃.

[0061] Measurements showed that the average grain size of the copper flat wire prepared in this comparative example was 20.5 μm, with a relatively large size distribution ranging from 15 to 70 μm. The copper flat wire prepared in this comparative example had a conductivity of 101.8% IACS, a yield strength of 185 MPa, a tensile strength of 247 MPa, and an elongation of 14%. It is evident that, compared to Example 1, the strength and elongation of the copper flat wire prepared in this comparative example are significantly reduced, failing to meet the requirements for copper conductors in ultra-high voltage / extra-high voltage transformer windings.

[0062] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing high-purity oxygen-free copper flat wire, characterized in that, Includes the following steps: S1. High-purity oxygen-free copper rods are subjected to continuous extrusion with equal diameter. After large shear deformation, the diameter of the copper rod remains unchanged to obtain ultrafine-grained copper rods. S2. The ultrafine-grained copper rod is continuously extruded to obtain fine-grained copper flat wire; S3. The fine-grained copper flat wire is subjected to room temperature small deformation drawing to obtain a copper flat wire with uniform structure at the edge and the core. S4. Perform recovery annealing on the flat wire after room temperature deformation to obtain a copper flat wire with matching mechanical and electrical properties; In step S1, the continuous extrusion temperature is 100-200℃, the extrusion roller speed is 10-15 rpm, and the shear deformation is 80-95%. In step S2, the temperature of the continuous extrusion is 400-600℃, the speed of the extrusion roller is 15-20 rpm, and the total deformation is over 90%. In step S3, drawing deformation is performed at room temperature, with a per-pass deformation of 13-17% and a total deformation not exceeding 35%. In step S4, the temperature of the recovery annealing is 120-250℃, and the holding time is 20-40 minutes.

2. The method for preparing high-purity oxygen-free copper flat wire according to claim 1, characterized in that, In step S1, the high-purity oxygen-free copper rod is prepared by the upward drawing method, and the specific process is as follows: The cleaned electrolytic copper plates are evenly fed into an industrial frequency induction furnace for melting at a temperature of 1240-1460℃. The melt is covered with charcoal to a thickness of 40-60mm. The resulting molten copper is then diverted to a holding furnace, where the temperature is controlled at 1120-1150℃. After cooling in a crystallizer, copper rods with a diameter of 8mm-15mm are drawn out.

3. A high-purity oxygen-free copper flat wire, characterized in that, Made by the method of claim 1 or 2.

4. The high-purity oxygen-free copper flat wire according to claim 3, characterized in that, The high-purity oxygen-free copper flat wire has a copper content ≥99.997wt.%, an oxygen content ≤3ppm, and the sum of other impurities ≤20ppm.

5. The high-purity oxygen-free copper flat wire according to claim 3, characterized in that, The high-purity oxygen-free copper flat wire has a room temperature conductivity of not less than 101% IACS, a yield strength of ≥240MPa, a tensile strength of ≥320MPa, and an elongation of ≥15%.

6. The application of the high-purity oxygen-free copper flat wire according to any one of claims 3-5 in ultra-high voltage / extra-high voltage transformers.

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